Safety syringe

ABSTRACT

A safety syringe ( 100; 700; 1200 ) comprising: a barrel ( 104; 704; 1204 ) having an opening at an end thereof; a syringe plunger ( 108; 708; 1208 ) configured to move within the barrel such that an inward stroke of the syringe plunger causes a substance within the barrel to be expelled from the opening; and a sheath ( 112; 712; 1212 ) configured to cover at least partially the opening in the barrel after use of the syringe, wherein the sheath is coupled to the syringe plunger and is configured to decouple from the syringe plunger at a point on the inward stroke such that the sheath is moveable independently of the syringe plunger and further movement of the sheath after decoupling at least partially covers the opening in the barrel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/913,243 filed Mar. 6, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/322,954, filed on Dec. 29, 2016, which is anational stage entry of International Application No. PCT/EP2015/069212filed Aug. 21, 2015, which claims priority to British Patent ApplicationSerial No. GB 1414911.6, filed Aug. 21, 2014, British Patent ApplicationSerial No. GB 1421187.4, filed Nov. 28, 2014, and British PatentApplication Serial No. GB 1508153.2, filed May 13, 2015, all of whichare hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to safety syringes and devices for fitting tosyringes to convert them to safety syringes. In particular embodiments,the invention relates to, but is not limited to, passive safety syringesand associated devices.

BACKGROUND

Broadly, syringes comprise a barrel having a hypodermic needle at oneend and a plunger configured to move within the barrel such that aninward stroke of the plunger causes a substance contained within thebarrel to be expelled from the needle.

Safety syringes typically include some form of safety mechanism toprotect healthcare workers from the hypodermic needle after it has beeninjected into a patient. Exemplary safety syringes may include a sheathfor covering the needle, or may cause the needle to retract within thebarrel of the syringe.

Safety syringes may be broadly split into ‘active’ and ‘passive’. Activesafety syringes typically require some action by a user of the syringeto engage the safety mechanism. Such action may be taken after removalof the needle from the patient, or may be taken during removal of theneedle from the patient. Typically, the action required to engage thesafety mechanism is separate from the action required to cause theinward stroke of the plunger. Passive safety syringes typically engagethe safety mechanism without any specific action by the user, that is,without any action other than that usually taken to use the syringe.

Known safety syringes comprise a spring-loaded safety mechanism that maybe engaged by the healthcare worker after the inward stroke of theplunger. The spring force urges a surface against the skin of thepatient, thereby extracting the needle and simultaneously engaging thesafety mechanism. Such devices are prone to misuse as the spring-loadedmechanism causes discomfort and bruising to patients when it isactivated. Therefore, healthcare workers are known to remove the needlefrom the patient before engaging the safety mechanism. This exposes thehealthcare worker to the needle after use and the spring-loaded actionof the safety mechanism may lead to blood splatter from the needle.

Other known safety syringes require the needle to be removed from thepatient before the safety mechanism may be engaged. This exposes thehealthcare worker to the needle after use.

SUMMARY

According to the invention in one aspect, there is provided a safetysyringe comprising: a barrel having an opening at an end thereof; asyringe plunger configured to move within the barrel such that an inwardstroke of the syringe plunger causes a substance within the barrel to beexpelled from the opening; and a sheath configured to cover at leastpartially the opening in the barrel after use of the syringe, whereinthe sheath is coupled to the syringe plunger and is configured todecouple from the syringe plunger at a point on the inward stroke suchthat the sheath is moveable independently of the syringe plunger andfurther movement of the sheath after decoupling at least partiallycovers the opening in the barrel.

Optionally, the sheath is configured to move along an exterior of thebarrel during the inward stroke of the syringe plunger and to decouplefrom the syringe plunger at or before a point at which the sheath passesof the opening in the barrel.

Optionally, the point on the inward stroke of the syringe plunger is theend of the inward stroke of the syringe plunger.

Optionally, the safety syringe further comprises a decoupling mechanismconfigured to decouple the sheath and the syringe plunger by way of theforce applied to the syringe plunger on its inward stroke.

Optionally, the sheath forms part of a safety plunger and wherein thedecoupling mechanism comprises a lug on the syringe plunger configuredto move between engagement and disengagement with a coupling recess inthe safety plunger.

Optionally, the lug of the syringe plunger is configured to disengagefrom the coupling recess of the safety plunger by rotation of thesyringe plunger relative to the safety plunger.

Optionally, the body of the syringe plunger comprises a rotation surfaceconfigured to engage with a reaction surface to rotate the plunger,wherein the reaction surface is fixed with respect to the barrel.

Optionally, the safety syringe further comprises a locking mechanismconfigured to lock the sheath in a position at least partially coveringthe opening of the barrel.

Optionally, the lug is configured to engage with a return recess in thesafety plunger at the end of the inward stroke of the safety plunger.

Optionally, the safety syringe further comprises a resilientlydeformable syringe plunger tip configured to compress against aninternal surface of the barrel proximal an end comprising the opening,thereby providing a biasing force urging the syringe plunger outward.

Optionally, the syringe plunger is configured such that the biasingforce causes outward movement and reverse rotation of the syringeplunger to move the lug into the return recess.

Optionally, the lateral extent of the return recess is less than thelateral extent of the coupling recess preventing full reverse rotationof the syringe plunger.

Optionally, the safety syringe comprises a locking channel comprisingthe coupling recess and the return recess connected by a substantiallylongitudinal channel, and wherein the locking channel is configured toguide the lug during activation of the locking mechanism.

Optionally, the lug is configured to meet an end of the substantiallylongitudinal channel at the end of the inward stroke of the safetyplunger thereby compressing the resiliently deformable tip of thesyringe plunger.

Optionally, the safety plunger extends beyond a head of the syringeplunger and a head of the safety plunger is connected to the sheath byat least one arm, the head for applying force by a user to cause theinward stroke of the safety plunger.

Optionally, the syringe further comprises a guard positioned between thehead of the syringe plunger and the head of the safety plunger.

Optionally, the guard comprises a rod extending between the head of thesafety plunger and the head of the syringe plunger, wherein the rod isconfigured to enter the syringe plunger after decoupling of the sheathand the syringe plunger.

Optionally, the safety syringe further comprises a hypodermic needleconnected to the opening in the barrel, and wherein the sheath isconfigured to cover at least partially the hypodermic needle after useof the syringe. The safety syringe may be a cannula or other form ofsyringe not including a needle.

According to the invention in a further aspect, there is provided asheath for use with a syringe, the syringe comprising a barrel having anopening at an end thereof and a syringe plunger configured to movewithin the barrel such that an inward stroke of the syringe plungercauses a substance within the barrel to be expelled from the opening,wherein the sheath is coupled to the syringe plunger and comprises adecoupling means for decoupling the sheath from the syringe plunger at apoint on the inward stroke such that the sheath is moveableindependently of the syringe plunger and further movement of the sheathafter decoupling at least partially covers the opening in the barrel.

According to the invention in a further aspect, there is provided asafety syringe comprising: a barrel having an opening at an end thereof;a syringe plunger configured to move within the barrel to cause asubstance within the barrel to be expelled from the opening; a safetyplunger coupled to the syringe plunger such that an inward stroke of thesafety plunger causes the syringe plunger to move within the barrel; anda sheath configured to cover at least partially the opening in thebarrel after use of the syringe, wherein the safety plunger isconfigured to couple to the sheath at a first point on the inward strokeand is configured to decouple from the syringe plunger at a second pointon the inward stroke such that the safety plunger is moveableindependently of the syringe plunger, and wherein further movement ofthe safety plunger after the first and second points on the inwardstroke causes the sheath at least partially to cover the opening in thebarrel.

Optionally, the first point on the inward stroke is the outermost pointon the inward stroke, such that the safety plunger is coupled to thesyringe plunger at the beginning of the inward stroke.

Optionally, the sheath is fixedly coupled to the safety plunger.

Optionally, the first point on the inward stroke is one of: before thesecond point on the inward stroke; after the second point on the inwardstroke; and at substantially the same location as the second point onthe inward stroke.

Optionally, the sheath comprises a sheath retaining means configured tofix the sheath with respect to the barrel, and operable to be releasedto allow movement of the sheath with respect to the barrel.

Optionally, the safety plunger is configured to release the retainingmechanism at a third point on the inward stroke.

Optionally, the safety syringe further comprises a coupling lockingmeans for locking the safety plunger and the sheath in a coupledconfiguration.

Optionally, the safety plunger is configured to move along an exteriorof the barrel during its inward stroke and to decouple from the syringeplunger at or before a point at which the sheath passes the opening inthe barrel.

Optionally, the second point on the inward stroke is substantially thepoint at which the syringe plunger has reached the end of the barrel.

Optionally, the safety syringe further comprises a decoupling mechanismconfigured to decouple the safety plunger and the syringe plunger.

Optionally, the decoupling mechanism is configured to decouple thesafety plunger and the syringe plunger under rotation of the syringeplunger relative to the safety plunger.

Optionally, the decoupling mechanism is configured to decouple thesafety plunger and the syringe plunger by way of the force applied tothe safety plunger on its inward stroke.

Optionally, the decoupling mechanism comprises a lug on the syringeplunger configured to move between engagement and disengagement with acoupling recess in the safety plunger.

Optionally, the lug of the syringe plunger is configured to disengagefrom the coupling recess of the safety plunger by rotation of thesyringe plunger relative to the safety plunger.

Optionally, a body of the syringe plunger comprises a rotation surfaceconfigured to engage with a reaction surface to rotate the plunger,wherein the reaction surface is fixed with respect to the barrel.

Optionally, the safety syringe further comprises a locking mechanismconfigured to lock the sheath in a position at least partially coveringthe opening of the barrel.

Optionally, the locking mechanism comprises the lug and a return recessin the safety plunger, wherein the lug is configured to engage with thereturn recess at the end of the inward stroke of the safety plunger.

Optionally, the locking mechanism is a biased locking mechanism, thesafety syringe further comprising a biasing member configured to providea biasing force causing outward movement and reverse rotation of thesyringe plunger to move the lug into the return recess.

Optionally, the biasing member comprises a resiliently deformablesyringe plunger tip configured to compress against an internal surfaceof the barrel proximal an end comprising the opening.

Optionally, the lateral extent of the return recess is less than thelateral extent of the coupling recess, for preventing full reverserotation of the syringe plunger.

Optionally, the safety syringe comprises a locking channel comprisingthe coupling recess and the return recess connected by a substantiallylongitudinal channel, and wherein the locking channel is configured toguide the lug during activation of the biased locking mechanism.

Optionally, the lug is configured to meet an end of the substantiallylongitudinal channel after the end of the inward stroke of the safetyplunger, thereby compressing the resiliently deformable tip of thesyringe plunger.

Optionally, the locking mechanism comprises a projection configured toenter a locking recess, wherein one of the projection and the lockingrecess is fixed in relation to the barrel and the other of theprojection and the locking recess is located on the safety plunger orthe sheath such that when the projection is located within the lockingrecess, the sheath is locked in a position at least partially coveringthe opening of the barrel.

Optionally, the projection is biased towards the locking recess suchthat the projection is urged into the locking recess upon alignment ofthe projection and the locking recess.

Optionally, during at least part of the inward stroke of the safetyplunger, the projection is configured to ride over a surface until theprojection and the locking recess are aligned, and wherein the biasingof the projection towards the locking recess exerts a frictional forceon the safety plunger during the inward stroke.

Optionally, the projection comprises a resiliently deformable prong.

Optionally, the safety syringe comprises a rate controlling means forlimiting and/or controlling a rate of travel of the safety plunger afterthe second point on the inward stroke.

Optionally, the rate controlling means comprises a rate limiting member,coupled to the safety plunger and configured to engage with the syringeplunger after the second point on the inward stroke.

Optionally, the rate limiting member comprises a first screw thread andthe syringe plunger comprises a second screw thread that is configuredto engage with the first screw thread to rotate the syringe plunger onfurther movement of the safety plunger after the second point on theinward stroke.

Optionally, the safety syringe further comprises a rotation preventionmember configured to prevent rotation of the syringe plunger from thefirst to the second points on the inward stroke.

Optionally, the rotation prevention member comprises an aperture throughwhich the syringe plunger passes, wherein the aperture comprises firstkeying features configured to correspond to second keying features onthe syringe plunger.

Optionally, the syringe plunger is configured such that the secondkeying features disengage from the first keying features at the secondpoint along the inward stroke.

Optionally, the syringe plunger is configured to pass through theaperture completely at the second point on the inward stroke.

Optionally, the safety syringe further comprises a resilientlydeformable bung within the barrel.

Optionally, the resiliently deformable bung is configured to rotate whenthe syringe plunger rotates, and wherein the bung has a diameter greaterthan an inner diameter of the barrel, such that a friction force resistsrotation of the bung and the syringe plunger.

Optionally, the resiliently deformable bung is configured to allowrelative rotation between the resiliently deformable bung and thesyringe plunger, and wherein a friction force between the syringeplunger and the resiliently deformable bung resists rotation of the bungand the syringe plunger.

Optionally, the rate controlling means comprises a resilientlydeformable rate controlling projection configured to be deformed by adeforming surface after the second point on the inward stroke, therebygenerating a friction force resisting further movement of the safetyplunger.

Optionally, the resiliently deformable rate controlling projectionprojects radially inwardly towards a longitudinal axis of the safetysyringe, and wherein the deforming surface is located on the safetyplunger and comprises a tab extending outwardly away from thelongitudinal axis of the safety syringe.

Optionally, the safety plunger extends beyond a head of the syringeplunger, and wherein a head of the safety plunger comprises at least onearm, the head of the safety plunger for applying force by a user tocause the inward stroke of the safety plunger.

Optionally, the safety syringe further comprises a guard positionedbetween the head of the syringe plunger and the head of the safetyplunger.

Optionally, the guard comprises a rod extending between the head of thesafety plunger and the head of the syringe plunger, wherein the rod isconfigured to enter the syringe plunger after decoupling of the safetyplunger and the syringe plunger.

Optionally, the safety syringe further comprises a hypodermic needleconnected to the opening in the barrel, and wherein the sheath isconfigured to cover at least partially the hypodermic needle after useof the syringe.

According to the invention in a further aspect, there is provided asafety syringe apparatus or use with a syringe, the syringe comprising abarrel having an opening at an end thereof and a syringe plungerconfigured to move within the barrel to cause a substance within thebarrel to be expelled from the opening, wherein the safety syringeapparatus comprises: a safety plunger configured to be coupled to thesyringe plunger such that an inward stroke of the safety plunger causesthe syringe plunger to move within the barrel; and a sheath configuredto cover at least partially the opening in the barrel after use of thesyringe, wherein the safety plunger is configured to couple to thesheath at a first point on the inward stroke and is configured todecouple from the syringe plunger at a second point on the inward strokesuch that the safety plunger is moveable independently of the syringeplunger, and wherein further movement of the safety plunger after thefirst and second points on the inward stroke causes the sheath at leastpartially to cover the opening in the barrel.

According to the invention in a further aspect, there is provided a kitof parts comprising: a safety plunger configured to be coupled to asyringe plunger of a syringe such that an inward stroke of the safetyplunger causes the syringe plunger to move within the barrel; and asheath configured to cover at least partially an opening in a barrel ofthe syringe after use of the syringe, wherein the safety plunger isconfigured to couple to the sheath at a first point on the inward strokeand is configured to decouple from the syringe plunger at a second pointon the inward stroke such that the safety plunger is moveableindependently of the syringe plunger, and wherein further movement ofthe safety plunger after the first and second points on the inwardstroke causes the sheath at least partially to cover the opening in thebarrel.

Optionally, the safety plunger is configured to be coupled to thesheath.

Optionally, the kit of parts further comprises a handle portionconfigured to be coupled to the barrel and to receive the safetyplunger, such that the safety plunger is able to pass through the handleportion.

Optionally, the kit of parts further comprises a syringe.

According to the invention in a further aspect, there is provided asafety syringe comprising: a barrel having an opening at an end thereof;a syringe plunger configured to move within the barrel to cause asubstance within the barrel to be expelled from the opening; a safetyplunger coupled to the syringe plunger such that an inward stroke of thesafety plunger causes the syringe plunger to move within the barrel; asheath configured to cover at least partially the opening in the barrelafter use of the syringe, wherein the safety plunger is configured tocouple to the sheath at a first point on the inward stroke; a decouplingmechanism configured to decouple the safety plunger from the syringeplunger under rotation of the syringe plunger relative to the safetyplunger at a second point on the inward stroke such that the safetyplunger is moveable independently of the syringe plunger, whereinfurther movement of the safety plunger after the first and second pointson the inward stroke causes the sheath at least partially to cover theopening in the barrel.

According to the invention in another aspect, there is provided a kit ofparts comprising: a safety plunger; a syringe plunger, wherein thesafety plunger is configured to be coupled to the syringe plunger suchthat an inward stroke of the safety plunger causes the syringe plungerto move within a barrel of a syringe; and a sheath configured to coverat least partially the opening in the barrel after use of the syringe,wherein, when the safety plunger, syringe plunger and the sheath areconnected, the safety plunger is configured to couple to the sheath at afirst point on the inward stroke and is configured to decouple from thesyringe plunger at a second point on the inward stroke such that thesafety plunger is moveable independently of the syringe plunger, andwherein further movement of the safety plunger after the first andsecond points on the inward stroke causes the sheath at least partiallyto cover the opening in the barrel.

Optionally, the kit of parts further comprises a handle portionconfigured to be connected to the safety plunger and to allow the safetyplunger to pass through.

According to the invention in another aspect, there is provided a kit ofparts comprising: a sub-assembly comprising a safety plunger and asyringe plunger, wherein the safety plunger is configured to be coupledto the syringe plunger such that an inward stroke of the safety plungercauses the syringe plunger to move within a barrel of a syringe; and asheath configured to cover at least partially the opening in the barrelafter use of the syringe, wherein, when the sub-assembly and the sheathare connected, the safety plunger is configured to couple to the sheathat a first point on the inward stroke and is configured to decouple fromthe syringe plunger at a second point on the inward stroke such that thesafety plunger is moveable independently of the syringe plunger, andwherein further movement of the safety plunger after the first andsecond points on the inward stroke causes the sheath at least partiallyto cover the opening in the barrel.

Optionally, the sub-assembly further comprises a handle portionconfigured to allow the safety plunger to pass through.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a safety syringe with the plungerextended;

FIG. 2A is an isometric view of a safety syringe with the plungerextended;

FIG. 2B is a schematic view of a position of a locking mechanismcorresponding to the position of the plunger in FIG. 2A;

FIG. 3A is an isometric view of a safety syringe with the plunger in afirst position along its inward stroke;

FIG. 3B is a schematic view of a position of a locking mechanismcorresponding to the position of the plunger in FIG. 3A;

FIG. 4A is an isometric view and partial section of a safety syringewith the plunger in a second position along its inward stroke;

FIG. 4B is a schematic view of a position of a locking mechanismcorresponding to the position of the plunger in FIG. 4A;

FIG. 5A is an isometric view of a safety syringe with the plunger in athird position along its inward stroke;

FIG. 5B is a schematic view of a position of a locking mechanismcorresponding to the position of the plunger in FIG. 5A;

FIG. 6A is an isometric view of a safety syringe with the plunger in afourth position along its inward stroke;

FIG. 6B is a schematic view of a position of a locking mechanismcorresponding to the position of the plunger in FIG. 6A;

FIG. 7 is a side elevation of a safety syringe;

FIG. 8 is an isometric view of a safety syringe;

FIG. 9 is an isometric view of a plunger;

FIG. 10 is an isometric view of a plunger;

FIG. 10A is an isometric view of a plunger;

FIG. 11 is a section through a plunger;

FIG. 12 is a side elevation of a safety syringe;

FIG. 13 is an exploded isometric view of a syringe plunger and safetyplunger;

FIGS. 13A and 13B show isometric views of a handle portion and a syringeplunger;

FIG. 14A is an isometric view of a safety syringe with a plunger in afirst position along its inward stroke;

FIG. 14B is a section through a sheath retaining means in a positioncorresponding to the position of the plunger in FIG. 14A;

FIG. 15A is an isometric view of a safety syringe with a plunger in asecond position along its inward stroke;

FIG. 15B is a section through a sheath retaining means in a positioncorresponding to the position of the plunger in FIG. 15A;

FIG. 16A is an isometric view of a safety syringe with a plunger in athird position along its inward stroke;

FIG. 16B is a section through a sheath locking means in a lockedposition;

FIG. 17 shows a safety syringe comprising a locking mechanism;

FIG. 18A is an isometric view of a safety syringe with a plunger in afirst position along its inward stroke;

FIG. 18B is an isometric view of a safety syringe with a plunger in asecond position along its inward stroke;

FIG. 18C is an isometric view of a safety syringe with a plunger at theend of its inward stroke;

FIG. 19A is a section through a safety syringe with a plunger in a firstposition along its inward stroke;

FIG. 19B is a section through a safety syringe with a plunger in asecond position along its inward stroke;

FIG. 19C is a section through a safety syringe with a plunger at the endof its inward stroke;

FIG. 20A is a plan view of a handle portion;

FIG. 20B is an isometric view of a handle portion and a syringe plunger;

FIG. 20C is a section through a handle portion and a syringe plunger;

FIG. 21A is an isometric view of a safety syringe with a plunger in afirst position along its inward stroke;

FIG. 21B is an isometric view of a safety syringe with a plunger in asecond position along its inward stroke;

FIG. 21C is an isometric view of a safety syringe with a plunger at theend of its inward stroke;

FIG. 22A is a section through a safety syringe with a plunger in a firstposition along its inward stroke;

FIG. 22B is a section through a safety syringe with a plunger in asecond position along its inward stroke; and

FIG. 22C is a section through a safety syringe with a plunger at the endof its inward stroke.

DETAILED DESCRIPTION

Generally, disclosed herein are safety syringes, methods of using safetysyringes and safety syringe devices in which the sheath is moved intoposition at least partially covering a needle of the syringe under aforce applied by the user. In exemplary safety syringes the sheath iscoupled to the plunger and a force is applied by a user to the sheaththereby moving the plunger and the sheath together. At a point along theinward stroke of the plunger, the sheath decouples from the plunger andcontinued application of force by the user moves the sheath to aposition at least partially covering the needle. A safety syringe deviceencompasses an apparatus configured to be fitted to a syringe in orderto make the syringe a safety syringe. That is, exemplary safety syringedevices may be the same as the safety syringes described herein andshown in the figures with the barrel, needle and/or syringe plungerremoved.

The ‘inward stroke’ is a stroke of a plunger longitudinal with respectto the syringe that is toward an open end of the barrel, that is, in adirection to expel a substance from the barrel. Outward has an oppositemeaning.

Referring to FIG. 1, a safety syringe 100 comprises a hypodermic needle102 fixed to an end of a barrel 104. The hypodermic needle is hollow.The barrel 104 comprises an opening at the point where the needle 102 isfixed to it such that a fluid path exists between the barrel 104 and thehollow channel of the needle 102. The syringe 100 further comprises asafety syringe apparatus comprising a handle portion 106 fixed inrelation to the barrel 104, a safety plunger 110 and a sheath 112.

A syringe plunger 108 is positioned inside the barrel 104 and isconfigured to move therein. The syringe plunger 108 may move on aninward stroke wherein the syringe plunger 108 moves further into thebarrel 104, or an outward stroke wherein the syringe plunger 108 isdrawn out of the barrel 104. The syringe plunger 108 is configured suchthat the inward stroke causes a substance held in the barrel 104 to beexpelled from the open end of the barrel 104 and through the needle 102.

In the exemplary apparatus of FIG. 1, the safety plunger 110 is coupledto the sheath 112 and comprises a head 114 and arms 116 a, 116 bconnecting the head 114 to the sheath 112. The arms 116 a, 116 b aremoveable along the outside of the barrel 104 such that the sheath 112moves along the outside of the barrel 104 on application of a force tothe head 114. In exemplary safety syringes and safety syringe apparatus,the safety plunger 110 may be manufactured as a plurality of separatefeatures that can be assembled later. For example, the sheath 112 may bemanufactured as one piece and the arms 116 a, 116 b and head 114 may bemanufactured as one piece. During assembly, the two pieces may be joinedtogether by some connection means, such as an interference or snap fitarrangement. Manufacturing the safety plunger 110 in a plurality ofpieces means that overall assembly of the safety syringe is made easier,as the safety plunger 110 may be assembled around the syringe plunger108 rather than having to guide the syringe plunger 108 into the safetyplunger 110. In addition, the safety plunger and the sheath may beseparate units capable of independent movement during at least part ofthe inward stroke of the safety syringe. An example of such anarrangement is shown in FIGS. 14 to 16 and described in detail below.

The needle 102 may be any type suitable for the task to be undertaken bythe user, such as injecting a drug into a patient or taking a fluid froma patient. In exemplary safety syringes 100, the needle 102 is fixedlyattached to the open end of the barrel 104. In other exemplary safetysyringes 100, the needle 102 may be removably attached to the barrel104. In such safety syringes 100, the needle 102 may be replaced byother needles of the same or a different type.

The barrel 104 is tapered at the open end towards the point at which theneedle 102 is connected. In the exemplary safety syringe 100 of FIG. 1,the barrel 104 comprises a tapered internal surface 118. As will beexplained later, the tapered internal surface may receive and therebycompress a resiliently deformable plunger tip fitted to the syringeplunger 108. The barrel 104 may be prefilled with a substance, forexample a medicament, such that the safety syringe 100 is ready to usefrom the packet.

The handle portion 106 comprises a main body 120 and flanges 122 a, 122b extending laterally from the main body 120. The main body 120comprises a portion that surrounds the barrel 104 and is fixed thereto.The flanges 122 a, 122 b are configured to receive the index finger andmiddle finger of a user while the thumb applies a force to the head 114of the safety plunger 110, although any combination of fingers and/orthumb could be used. The handle portion 106 is fixed to the barrel 104by an aperture 124 configured to receive a radially protruding lip of anopening of the barrel at a distal end to the opening coupled to theneedle 102. The lip may be received by way of a snap fit to hold it inthe aperture 124.

The sheath 112 may be at least partially received within the main body120 of the handle portion 106 when the syringe plunger 108 is at theoutermost part of its stroke.

The arms 116 a, 116 b of the safety plunger 110 are configured to passthrough the handle portion 106 such that the safety plunger 110 may movein its stroke relative to the handle portion 106 and, therefore, thebarrel 104. The sheath 112 is configured to travel along the outside ofthe barrel 104 with the inward stroke of the safety plunger 110 untilthe sheath 112 at least partially covers the needle 102. At theinnermost point of the stroke of the safety plunger 110, the end 126 ofthe sheath 112 is beyond the end of the needle 102, such that the sharppoint of the needle 102 is not exposed.

The arms 116 a, 116 b comprise coupling recesses 128 a, 128 b (onlycoupling recess 128 b can be seen in FIG. 1). The syringe plunger 108comprises lugs 130 a, 130 b (only lug 130 b can be seen in FIG. 1)configured to be received in coupling recesses 128 a, 128 b. The lugsare on a head 132 of the syringe plunger 108, which is located at anouter end of the syringe plunger 108. The lugs 130 a, 130 b and couplingrecesses 128 a, 128 b are configured such that rotation of the syringeplunger 108 may engage and disengage the lugs 130 a, 130 b within thecoupling recesses 128 a, 128 b. When the lugs 130 a, 130 b are engagedin the coupling recesses 128 a, 128 b, the safety plunger 110 is coupledto the syringe plunger 108. When the lugs 130 a, 130 b are disengagedfrom the coupling recesses 128 a, 128 b, the safety plunger 110 isdecoupled from the syringe plunger 108.

The syringe plunger 108 comprises a rotation surface 134. The rotationsurface is configured to interact with a reaction surface (not shown inFIG. 1) to rotate the syringe plunger 108. The rotation surface may be aramped or angled portion of the syringe plunger 108. The reactionsurface is fixed with respect to the barrel 104. In the exemplaryembodiment of FIG. 1, the syringe plunger 108 has a cross-shaped sectionalong its body. The handle portion 106 comprises a cross-shaped aperturecorresponding to the cross-shape of the syringe plunger 108. As thesyringe plunger 108 passes along its stroke, the cross-shaped body ofthe syringe plunger 108 passes through the cross shaped aperture of thehandle portion 106. The rotation surface 134 comprises an angled portionof the cross-shape of the body of the syringe plunger 108. Eachextension of the cross-shaped body is so angled. The effect is that whenthe rotation surface 134 reaches the cross-shaped aperture in the handleportion 106, the syringe plunger 108 is rotated. Other methods ofrotating the syringe plunger 108 are possible and some are discussedherein.

The stroke of the safety plunger 110 is greater in length than thestroke of the syringe plunger 108, as the arms 116 a, 116 b extendbeyond the head 132 of the syringe plunger 108. Therefore, a gap 136exists between the head 114 of the safety plunger and the head 132 ofthe syringe plunger. As explained below, a guard may be positioned toprevent a user inserting a finger or thumb into the gap 136 and applyinga force directly to the head 132 of the syringe plunger 108.

FIGS. 2A-6A show isometric views of a safety syringe 100 at variouspositions along the inward stroke of the safety plunger 110 (andtherefore the syringe plunger 108 by way of the coupling of the two).The operation of the safety syringe 100 will be described below withreference to FIGS. 2A-6A.

FIG. 2A shows the safety syringe 100 with both the syringe plunger 108and the safety plunger 110 fully extended and at the outermost points oftheir strokes. The syringe plunger 108 is coupled to the safety plunger110, as the lugs 130 a, 130 b of the head 132 of the syringe plunger 108are engaged in the coupling recesses 128 a, 128 b in the arms 116 a, 116b of the safety plunger. In this way, the syringe plunger 108 is coupledto the sheath 112, which forms part of the safety plunger 110. Thebarrel 104 may be prefilled with a substance, such as a medicament.

A user may place the index finger and middle finger of one hand againstthe flanges 122 a, 122 b of the handle portion 106 and the thumb of thesame hand on the head 114 of the safety plunger 110. The user thenapplies a relative force to the head 114 and the handle portion 106 byclosing the thumb towards the index and middle fingers. For the sake ofclarity, this relative force will be considered herein as a force on thehead 114.

The force applied to the head 114 begins the inward stroke of the safetyplunger 110. As the safety plunger 110 and the syringe plunger 108 arecoupled, the inward stroke of the syringe plunger 108 also begins. Thesafety plunger 110 and the syringe plunger 108 move together.

FIG. 3A shows the safety syringe 100 part way through the inward strokesof both the syringe plunger 108 and the safety plunger 110. The syringeplunger 108 and the safety plunger 110 have moved together under theforce applied to the head 114 to a point at which the rotation surface134 is about to interact with the reaction surface on the handle portion106.

Continued application of the force on the head 114 leads the syringeplunger 108 to decouple from the safety plunger, as shown in FIG. 4A. Toshow this more clearly, part of the safety syringe 100 has been cut awayin FIG. 4A. The rotation surface 134 that is angled with respect to thedirection of travel of the syringe plunger 108 has interacted with thereaction surface and the syringe plunger 108 has been rotated. As aresult, the lugs 130 a, 130 b (only lug 130 b is visible in FIG. 4A) onthe head 132 of the syringe plunger 108 have become disengaged from thecoupling recesses 128 a, 128 b in the arms 116 a, 116 b. The safetyplunger 110 is now free to move relative to the syringe plunger 108.That is, the safety plunger 110 is free to move while the syringeplunger 108 remains stationary. As set out above, the force applied bythe user to begin the strokes of the safety plunger 110 and the syringeplunger 108 is used to decouple the two. Continued application of forceto the head 114 will continue the inward stroke of the safety plunger110.

The point at which the decoupling occurs may be the point at which thesyringe plunger 108 has completed its inward stroke. That is, thedecoupling may occur at the innermost point of the stroke of the syringeplunger 108. This ensures that all of the substance contained within thebarrel 104 has been expelled from the syringe 100 before decoupling. Itis noted once again that, in the exemplary apparatus of FIGS. 1 to 6,decoupling of the safety plunger 110 from the syringe plunger 108 leadsto decoupling of the sheath 112 from the syringe plunger 108, as thesheath forms part of the safety plunger 108.

FIG. 5A shows the continued travel of the safety plunger 110 withcontinued application of a force to the head 114. The safety plunger 110continues to pass through the handle portion 106 and continues to extendfurther down the length of the syringe 100. The sheath 112 has nowextended beyond the end of the barrel 104 and now partially covers theneedle 102.

As shown in FIG. 6A, when the inward stroke of the safety plunger 110has been completed, the head 114 abuts the handle portion 106 and alsoabuts the head 132 of the syringe plunger 108. In this position thesheath 112 has extended such that it completely surrounds the needle102. The end 126 of the sheath 112 extends beyond the tip of the needle102 such that the needle is not exposed. In this position, the safetysyringe 110 may lock in relation to the barrel 104 and needle 102, suchthat the needle 102 cannot become exposed. In exemplary safety syringes,the safety plunger 110 may become locked to the handle portion 106.

FIGS. 2B-6B show the operation of a locking mechanism for locking thesafety plunger 110 in a position in which the sheath 112 is covering theneedle 102. The locking mechanism locks the safety plunger 110 inrelation to the barrel 104 at the innermost point of the stroke of thesafety plunger 110. Herein, the locking mechanism shown in FIGS. 2B-6Bmay be termed a biased locking mechanism to help differentiate it fromother locking mechanisms, such as the snap fit locking mechanism shownin FIG. 17. As explained below, the biased locking mechanism may bebiased by a resiliently deformable tip of the syringe plunger, or by analternative outwardly biasing member.

Referring to FIG. 2B, one of the lugs 130 a, 130 b (from here onreferred to as 130 when describing the locking mechanism) is shown in achannel 138. The channel is formed in one of the arms 116 a, 116 b ofthe safety plunger. For the avoidance of doubt, it is noted that inexemplary embodiments, channels 138 may be formed in both arms 116 a,116 b.

In embodiments in which there is no locking mechanism or a differentlocking mechanism to that shown in FIGS. 2B-6B, only the coupling recess128 a, 128 b (from here on referred to as 128 when describing thelocking mechanism) may be formed in the arms 116 a, 116 b. Forillustrative purposes, the coupling recess 128 is shown in hatchedshading in FIGS. 2B-6B.

The channel 138 is substantially C-shaped. In exemplary lockingmechanisms, the channel 138 is a skewed C-shape. The channel comprisesthe coupling recess 128, a substantially longitudinal portion 140 and areturn recess 142. The lateral extent of the return recess 142 is lessthan the lateral extent of the coupling recess 128.

In FIG. 2B, the lug 130 is positioned in the coupling recess 128 and sothe safety plunger 110 and the syringe plunger 108 are coupled. Thelateral position of the lug 130 is that before twisting and is definedby the cross-shaped main body of the syringe plunger 108 and thecorresponding cross-shaped aperture in the handle portion. It is notedthat the lateral position of the lug 130 may be defined by other means.

In FIG. 3B, the safety plunger 110 has made part of its inward strokeand has reached a point just before decoupling from the syringe plunger108. The lug 130 is still positioned in the coupling recess 128.

In FIG. 4B, the inward stroke of the safety plunger 110 and the syringeplunger 108 have reached the point at which the syringe plunger 108 hasrotated. At this point, the lug 130 has disengaged from the couplingrecess 128 and the safety plunger 110 and syringe plunger are decoupled.This is shown in FIG. 4B by the lug 130 having exited the couplingrecess and entered the substantially longitudinal channel 140. Furtherinward motion of the safety plunger 110 will be independent of thesyringe plunger 108.

In FIG. 5B, the safety plunger 110 has traveled further along its inwardstroke independently of the syringe plunger 108, which has remainedstationary. Therefore, the lug 130 has traveled down the substantiallylongitudinal channel 140.

The syringe plunger comprises a resiliently deformable tip, which may becompressed at the end of the barrel 104 before the needle 102. Suchcompression results in a biasing force urging the syringe plunger 108back up the barrel 104 to begin its outward stroke. As the lug 130 meetsand is pushed against the end of the substantially longitudinal channel140, continued force applied to the head 114 of the safety plunger 110also applies a force to the syringe plunger 108 and compresses theresiliently deformable tip of the syringe plunger 108. In this way, thesyringe plunger 108 and the safety plunger 110 are temporarily recoupledto compress the resiliently deformable tip.

As the force is removed from the head 114 of the safety plunger, thebiasing force resulting from the compression of the resilientlydeformable tip begins to move the syringe plunger outward to begin itsoutward stroke. With outward movement of the syringe plunger 108, therotation surface 134 is configured to interact again with the or anotherreaction surface that is fixed in relation to the barrel 104 and thesyringe plunger begins to rotate back such that the lug 130 enters thereturn recess 142. This is shown in FIG. 6B. The lug 130 meets thelateral extent of the return recess 142 before the syringe plunger 108as rotated back fully, as the lateral extent of the return recess 142 isless than the lateral extent of the coupling recess 128.

As the lug 130 enters the return recess 142, it is prevented fromtraveling up the substantially longitudinal channel 140 and the safetyplunger 110 is locked to the syringe plunger 108. Any attempt theseparate the safety plunger 110 and syringe plunger 108 urges the lug130 further into the return recess, reinforcing the lock.

Further, the syringe plunger 108 is locked with respect to the barrel104 and cannot travel on its outward stroke. This is because the lug 130reaches the lateral extent of the return recess 142 before the syringeplunger 108 has fully rotated back and so the rotation surface 134 hasnot fully passed the reaction surface. The only way that the syringeplunger 108 can continue its outward stroke is if it continues torotate, but this is prevented by the lug 130 reaching the end of thereturn channel 142. Therefore, the syringe plunger 108 is locked in thebarrel 104 and, as it is locked to the syringe plunger 108, the safetyplunger 110 is also locked with respect to the barrel 104. This keepsthe sheath 112 in place covering the needle 102.

As set out above, the full inward stroke of the safety plunger fulfillstwo actions: the dispensing of the substance in the barrel 104 and thecovering of the needle 102 by the sheath 112. These two actions arecompleted with only a single action from the user.

Moreover, the single action for the user is entirely intuitive, as it isno different from the action required to use a standard syringe, that ofdepressing a plunger. The only difference is that the inward stroke isslightly longer. Further, healthcare professionals are trained always tocomplete the inward stroke when using syringes. Therefore, when actingout that training, a healthcare professional using the safety syringe100 would also engage the sheath 112 over the needle 102. As such, thesafety syringe 100 has improved safety.

Also, the action of completing the inward stroke of the safety plunger110 after decoupling from the syringe plunger 108 pushes the end surface126 of the sheath 112 against the skin of the patient and extracts theneedle 102 therefrom. This is done under a normal amount of forceapplied by a user that is steadily applied rather than the high forcerapidly applied by a spring in known safety syringes. Therefore,discomfort and bruising for the patient is reduced.

In exemplary safety syringes, the safety plunger 110 is free to movethrough the handle portion 106 with little or no resistance. Incontrast, the movement of the syringe plunger 108 in the barrel 104offers an amount of resistance. As a result, after decoupling of thesyringe plunger 108 from the safety plunger 110, there is a sharp dropoff in resistance and therefore the force required to move the safetyplunger 110 is lower when decoupled. This means that it is verydifficult for a user to stop the inward stroke before the sheath 112 hasextended beyond the tip of the needle, as it happens rapidly. In othersafety syringes, movement of the safety plunger 110 through the handleportion may be damped to offer some resistance.

In the above exemplary safety syringe 100, rotation of the syringeplunger 108 is used to decouple it from the safety plunger 110. However,there are many other ways in which this may be implemented and these arecovered within the scope of the appended claims. Mechanisms forimplementing the decoupling may include one or more of the following:

-   -   A rotational engagement, where the plunger is driven by a        horizontal slot or coupling recess in the safety plunger;    -   A clip engagement, where biased clips retain the plunger until        they are displaced by displacement surfaces fixed in relation to        the barrel;    -   A frangible engagement, wherein the syringe plunger and safety        plunger are moulded as one component and the small plastic        “bridge” that connects them is severed;    -   A magnetic engagement, in which magnets in the safety plunger        attract a metallic element in the syringe plunger (or vice        versa);    -   A string/rope/thread engagement, where the syringe plunger is        pulled by “tethers” on the safety plunger which are de-latched        or broken;    -   An interference engagement, in which the syringe plunger is        “wedged” into a bottle neck in the safety plunger and driven        forwards by friction;    -   An adhesive engagement, where a glue is used to couple the        syringe plunger and the safety plunger;    -   A suction engagement, whereby the syringe plunger is coupled to        the safety plunger by air    -   Electronics—electromagnetism, smart materials, computer        controlled latches may also be used;    -   A gear engagement; and    -   A ratchet engagement.

FIGS. 7 and 8 show a side elevation and isometric view of a safetysyringe 700 respectively. In FIG. 7, the syringe plunger 708 and thesafety plunger 710 are coupled by bias clips 740 a, 740 b arranged onthe internal faces of the arms 716 a, 716 b of the safety plunger 710.The clips 740 a, 740 b are biased towards a central axis of the safetysyringe 700 and are configured to retain the head 732 of the syringeplunger 708, such that the syringe plunger 708 and the safety plunger710 are coupled and, thereby, the syringe plunger 708 and the sheath 712are coupled.

Displacement surfaces 742 a, 742 b that are fixed in relation to thebarrel 704 are configured to displace the biased clips 740 a, 740 b asthey pass the displacement surfaces 742 a, 742 b. The displacement isaway from the central axis of the safety syringe 700 and therefore hasthe effect of releasing the head 732 of the syringe plunger 708. This,in turn, decouples the syringe plunger 708 from the safety plunger 710.As can be seen in FIG. 8, the arms 716 a, 716 b may comprise slots orrecesses 744 a, 744 b into which the clips 740 a, 740 b may move whenthey are displaced.

In aspects other than the coupling/decoupling arrangement of the syringeplunger 708 and the syringe plunger 710, the safety syringe 700 maycomprise one or more features of the safety syringe 100.

FIG. 9 shows the syringe plunger 108 of FIG. 1 in isolation.

FIG. 10 shows an alternative syringe plunger 1008 that may be used whendecoupling of the syringe plunger from the safety plunger is by rotationof the syringe plunger. The syringe plunger 1008 may, for example, beused in the safety syringe 100 of FIG. 1. As can be seen in FIG. 10, themain body of the syringe plunger 1008 has a substantially rectangularcross section. A top portion of the syringe plunger 1008 is twisted withrespect to the main body such that a rotation surface 1034 is provided.In exemplary safety syringes, the syringe plunger 1008 may pass throughan aperture in the handle portion that corresponds to the cross sectionof the main body of the syringe plunger 1008. As the rotation surface1034 reaches the aperture, the syringe plunger 1008 is caused to rotateas the top portion is twisted. The syringe plunger 1008 also comprises ahead 1032 and lugs 1030 a, 1030 b thereon, which operate in a similarway to those described above.

FIG. 10A shows an exemplary syringe plunger 1008 a comprising a lostmotion device 1009. The lost motion device 1009 is configured tocompress, if needed, at the end of the barrel of a syringe to accountfor tolerances in the manufacture of the barrel. Tolerances in barrelmanufacture can be relatively high when compared with tolerances forother features of a safety syringe. As a result of this, a syringeplunger may reach the end of its inward stroke when the tip of thesyringe plunger has not reached the end of the barrel, leaving some ofthe substance in the barrel. In the case of drug delivery, this is to beavoided. Conversely, the tip of the syringe plunger may reach the end ofthe barrel before the decoupling means has decoupled the syringe plungerfrom the safety plunger, preventing the location of the sheath aroundthe needle.

Therefore, the syringe plunger may be manufactured to be slightly longerthan the barrel and a lost motion device 1009 positioned along itslength. The lost motion device is a compressible element in the syringeplunger 1008 a that compresses if the tip of the syringe plunger 1008 areaches the end of the barrel before the end of the inward stroke of thesyringe plunger 1008 a. This ensures that the tip of the syringe plunger1008 a always reaches the end of the barrel and that the decouplingmeans always activates.

The lost motion device 1009 may be a spring, as in FIG. 10A, but mayalso be any other compressible device or material, such as foam or anelastomeric material.

FIG. 11 shows a syringe plunger 1108 comprising a central bore 1146 inthe head 1132 that extends along the length of the syringe plunger 1108.The central bore 1146 may be incorporated into any of the syringeplungers covered within the scope of this document. The central bore1146 may be configured to receive a guard (mentioned above) that sits inthe gap 136 shown in FIG. 1. The guard may be a pin or rod attached tothe underside of the head 132 and aligned with the central bore 1146.The guard is configured to prevent a user inserting their thumb orfinger into the gap 136 and applying a force directly to the head 132 ofthe syringe plunger 108, as to do so could result in use of the safetysyringe 100 without deployment of the sheath 112.

FIG. 12 shows an exemplary safety syringe 1200. The safety syringe 1200comprises a decoupling mechanism that does not require a handle portionin order to operate. More specifically, the safety syringe 1200comprises a decoupling mechanism able to operate with only features ofthe safety plunger 1210 and the syringe plunger 1208. Such a decouplingmechanism may be provided in many ways and the safety syringe 1200 isone example.

The safety plunger 1210 comprises a laterally outwardly biased member1250. The biased member 1250 comprises two retaining lugs 1252 a, 1252 bbiased laterally outwardly and configured to engage with correspondingretaining means (e.g., recesses or apertures 1254 a, 1254 b) in thesyringe plunger 1208. As the syringe plunger 108 enters a barrel 1204 ofthe safety syringe, the internal walls of the barrel 1204 travel up theoutside of the syringe plunger 1208 until they interact with theretaining lugs 1252 a, 1252 b pushing them laterally inwards andovercoming the bias imparted by the biasing member 1250. Continuedlongitudinally inward force applied to the safety plunger 1210 forcesthe retaining lugs 1252 a, 1252 b over the corresponding retaining meansof the syringe plunger 1208 and decouples the safety plunger 1210 andthe syringe plunger 1208.

FIG. 13 shows an exemplary safety plunger 1310 and syringe plunger 1308.Together, the safety plunger 1310, syringe plunger 1308 and a barrel endcap 1360 are configured to rotate the syringe plunger 1308 at a point onthe inward stroke thereof. It is noted that there is no rotation surfaceon the syringe plunger 1308. The syringe plunger 1308 may be a standardsyringe plunger provided with a syringe and need not be specificallydesigned. It is also noted that there are many ways that rotation of thesyringe plunger 1308 relative to the safety plunger 1310 may be achievedand the exemplary arrangement in FIG. 13 shows one way. In a specificsafety syringe apparatus, one or more rotation surfaces may be locatedon the handle portion (e.g. on the finger flange) rather than on aseparate component, as in FIG. 13. For example, in FIGS. 13A and 13Brotation surfaces 1370 a, 1370 b are located on the handle portion 1306.The rotation surfaces 1370 a, 1370 b comprise angled surfaces configuredto interact with protrusions 1372 a, 1372 b on the syringe plunger 1308to rotate the syringe plunger 1308 as the protrusions 1372 a, 1372 bpass over the rotation surfaces 1370 a, 1370 b on the inward stroke ofthe syringe plunger 1308. The barrel end cap 1360 comprises across-shaped aperture 1362 configured to receive the cross-shaped crosssection of the syringe plunger 1308. Rotation of the syringe plunger1308 is provided through rotation of the barrel end cap 1360. For thispurpose, the barrel end cap comprises rotation lugs 1364 a, 1364 bconfigured to travel within rotation channels 1366 a, 1366 b in thesafety plunger 1310. As the safety plunger 1310 travels on its inwardstroke, the rotation lugs 1364 a, 1364 b travel through the rotationchannels 1366 a, 1366 b, which comprise angle sections that rotate thebarrel end cap 1360 with inward movement of the safety plunger 1310.Rotation of the barrel end cap 1360 rotates the syringe plunger 1308 andthereby decouples the syringe plunger 1308 from the safety plunger 1310,as discussed above.

FIGS. 14 to 16 show a syringe 1400 fitted with an exemplary safetysyringe apparatus 1401. As above, the syringe 1400 and the safetysyringe apparatus 1401 may together form a safety syringe. The safetysyringe apparatus 1401 comprises a safety plunger 1410 and a sheath1412. Many of the features of the syringe 1400 and the safety syringeapparatus 1401 are similar to those described above in respect of any ofthe other exemplary apparatus. As such, a description of those featuresis not given again here and corresponding reference numerals are used toidentify them in FIGS. 14 to 16.

Referring to FIG. 14A, the safety syringe apparatus 1401 is shown in anextended state. That is, the safety plunger 1410 and the syringe plunger1408 are at the outermost point of their inward strokes. The safetyplunger 1410 is coupled to the syringe plunger 1408 by way of lugs andcorresponding coupling recesses.

The sheath 1412 is initially decoupled from the safety plunger 1410 andis configured to couple to the safety plunger 1410 at a point on theinward stroke of the safety plunger 1410. After coupling of the sheath1412 and the safety plunger 1410, further inward movement of the safetyplunger 1410 results in movement of the sheath 1412 towards and over theend of the barrel of the syringe 1400 and the hypodermic needle 1402.

Initially, the sheath 1412 is fixed with respect to the syringe 1400 bya sheath retaining means 1470, which is shown in greater detail in FIG.14B and described below.

An end 1426 of the sheath 1412 is substantially level with a point onthe syringe 1400 at which the hypodermic needle 1402 begins, or a smalldistance, e.g. 1-5 mm back from that point. All of the hypodermic needleis exposed when the safety syringe apparatus 1401 is in its extendedstate.

In the exemplary safety syringe apparatus 1401 of FIGS. 14 to 16, thesheath 1412 comprises channels 1472 a, 1472 b (not shown). The channels1472 a, 1472 b correspond to arms 1416 a, 1416 b of the safety plunger1410 and are configured to allow travel of one of the arms 1416 a, 1416b within each channel 1472 a, 1472 b during the inward stroke of thesafety plunger 1410.

As shown in FIG. 14B, the exemplary sheath retaining means 1470comprises a sheath latch 1474. The sheath latch 1474 is engaged with asheath retaining lip 1476.

In exemplary safety syringe apparatus, the sheath retaining lip 1476 maybe part of a handle portion 1406 that is fixed with respect to thesyringe 1400. Therefore, when the sheath latch 1474 is engaged with thesheath retaining lip 1476, the sheath is fixed in relation to thesyringe 1400. The top surface of the sheath 1412 abuts the underside ofthe handle portion 1406, or could be modified to meet the underside ofthe syringe flange 1400. The sheath latch 1474 is held in positionengaged with the sheath retaining lip 1476 by a biasing force, in thiscase provided by a resiliently deformable sheath arm 1478 on which thesheath latch 1474 is located. There may be a plurality of sheathretaining means. For example, on opposed sides of the sheath 1412 (andhandle portion 1406).

FIG. 15A shows the safety syringe apparatus 1401 at a point on theinward stroke of the safety plunger 1410 at which the safety plunger1410 decouples from the syringe plunger 1408, as described above inrelation to other apparatus. In addition, the sheath retaining means1470 is released, such that the sheath 1412 is no longer fixed inrelation to the syringe 1400, which may occur at the same point in theinward stroke of the safety plunger 1410 as the point at which thesafety plunger 1410 decouples from the syringe plunger 1408.

The safety plunger 1410 is configured to release the sheath retainingmeans 1470 such that the sheath 1412 is able to move independently ofthe syringe 1400. For this purpose, the safety plunger 1410 comprisessheath releasing flanges 1480 a, 1480 b that are configured to interactwith the sheath latch 1474 to release the sheath retaining means 1470.Specifically, the sheath releasing flanges 1480 a, 1480 b compriseangled surfaces that contact the sheath latch 1474 as the safety plunger1410 travels on the inward stroke to overcome the biasing force holdingthe sheath latch 1474 in engagement with the sheath retaining lip 1476.

As can be seen in FIG. 15A, the arms 1416 a, 1416 b have been receivedin the channels 1472 a, 1472 b of the sheath 1412. End faces 1482 a,1482 b of the arms 1416 a, 1416 b is shown in FIG. 15A to be just shortof the ends of the channels 1472 a, 1472 b. Continued movement of thesafety plunger 1410 on its inward stroke results in contact between theend faces 1482 a, 1482 b with the ends of the channels 1472 a, 1472 b tocouple the safety plunger 1410 with the sheath 1412. Continued movementof the safety plunger 1410 after coupling with the sheath 1412 resultsin movement of the sheath 1412 down the barrel of the syringe 1400 andover the hypodermic needle 1402.

It is noted that the safety plunger 1410 couples to the sheath 1412 at afirst point (location) on the inward stroke of the safety plunger 1410and decouples from the syringe plunger 1408 at a second point (location)on the inward stroke of the safety plunger 1410. In addition, the safetyplunger 1410 is configured to release the sheath retaining means at athird point (location) on its inward stroke. However, the terms “first”,“second” and “third”, when used in this context need not indicate anorder in which the two points are reached on the inward stroke. Inparticular, in exemplary safety syringe apparatus, the first point maybe before the second point, the first point may be the same as thesecond point or the first point may be after the second point.

FIG. 16A shows the safety syringe apparatus 1401 after use when thesafety plunger 1410 has completed its inward stroke. The sheath 1412 isextended beyond the end of the barrel of the syringe 1400 to cover thehypodermic needle 1402.

As shown in FIG. 16B, the arms 1416 a, 1416 b of the safety plunger 1410have extended into the channels 1472 a, 1472 b of the sheath 1412 suchthat the end faces 1482 a, 1482 b of the arms 1416 a, 1416 b connectwith the ends of the channels 1472 a, 1472 b. In addition, a couplinglocking means 1484 locks the sheath 1412 and the safety plunger 1410 ina coupled state. In the exemplary safety syringe apparatus 1401 of FIG.16B, the coupling locking means 1484 comprises a latch on the arms 1416a, 1416 b that engages with a lip in the channels 1472 a, 1472 b.Engagement is provided by a biasing force applied by a resilience of thearms 1416 a, 1416 b.

FIG. 17 shows a safety syringe apparatus 1701 fitted to a syringe 1700comprising a locking mechanism that comprises a projection 1786configured to enter a locking recess 1788. Many of the features of theapparatus 1701 and syringe 1700 are similar to those described above inrespect of any of the other exemplary apparatus. As such, a descriptionof those features is not given again here and corresponding referencenumerals are used to identify them in FIG. 17.

In the exemplary locking mechanism of FIG. 17, the projection is fixedin relation to a barrel 1704 of a syringe 1700 to which the safetysyringe apparatus 1701 is fitted and the locking recess 1786 is locatedon the safety plunger 1710. It is noted that in other exemplary lockingmechanisms, the projection 1786 may be located on the safety plunger1710 and the locking recess 1788 may be fixed in relation to the barrel1704. Further, one of the projection 1786 or the locking recess 1788 maybe located on the sheath 1712 as opposed to the safety plunger 1710.There may be a plurality of projections and a plurality of lockingrecesses, as shown in FIG. 17.

The projection 1786 is urged towards the locking recess under a biasingforce. In the exemplary locking mechanism of FIG. 17, the biasing forceis provided by resilience in the projection 1786. That is, theprojection 1786 is a resiliently deformable prong.

The projection 1786 is urged towards the locking recess 1788 and entersthe locking recess 1788 when the locking recess 1788 and the projection1786 are aligned. Before alignment, the projection 1786 rides along anouter surface of an arm 1716 a, 1716 b of the safety plunger 1710. Theprojection 1786 therefore exerts the biasing force against the outersurface of the arm 1716 a, 1716 b. This force against the arm 1716 a,1716 b produces friction during travel of the safety plunger 1710 alongits inward stroke and increases the force required by a user to move thesafety plunger 1710 on its inward stroke. As the safety plunger, 1710 iscoupled to the syringe plunger, the force required to move the syringeplunger be also increased. The increase in required force may beconsidered to have a damping effect on the movement of the syringeplunger.

In the exemplary apparatus comprising a lost motion device, such as thelost motion device 1009 shown in FIG. 10A, the damping of the movementof the syringe plunger may provide a benefit in reducing the likelihoodof compressing the lost motion device at the beginning of the inwardstroke of the syringe plunger. As explained above, the lost motiondevice may be included at an end of the syringe plunger in order tocompensate for tolerances in manufacture of syringes. For this purpose,it is desirable that the lost motion device is compressed, as necessary,at the end of the inward stroke of the syringe plunger. However, if alarge force is exerted on the safety plunger 1710 (and therefore thesyringe plunger) then the resulting rapid build-up in pressure withinthe barrel 1704 of the syringe 1700 may compress the lost motion device,preventing it from compensating for manufacturing tolerances in thesyringe 1700. By exerting a frictional force on the safety plunger 1710,the projection 1786 of the locking mechanism absorbs some of the forceapplied by the user to the safety plunger 1710 and therefore educes theamount of force transferred to the liquid within the barrel 1704. Assuch, the pressure within the barrel does not increase as much and thisreduces the likelihood that the lost motion device will compress earlyin the inward stroke of the syringe plunger.

A storage recess 1790 is formed in the safety plunger 1710 foraccommodating the projection 1786 when the safety syringe apparatus 1701is extended and in a state that it may be stored. The storage recessprevents deformation of the projection 1786 over long periods while thesafety syringe apparatus 1701 is stored. This ensures the resilience ofthe projection 1786 is maintained.

Exemplary safety syringes disclosed herein may comprise rate controllingmeans for limiting and/or controlling (e.g. decreasing) a rate ofextraction of the syringe needle from a subject. In particular exemplarysafety syringes, the rate controlling means may be configured to limitand/or control the rate of depression of the safety plunger afterdecoupling from the syringe plunger. In exemplary safety syringes, thesyringe needle is extracted from the subject by a force applied to theskin of the subject by the sheath resulting from pressure applied to thesafety plunger after it is decoupled from the syringe plunger.Therefore, controlling and or limiting the rate of travel of the safetyplunger after such decoupling can limit and/or control the rate ofextraction of the syringe needle.

Such exemplary safety syringes limit discomfort felt by a subject as aresult of too rapid an extraction of the syringe needle. Limiting therate of extraction of the syringe needle also allows greater control ofthe safety syringe during extraction. If the rate of extraction isuncontrolled and therefore sudden then this can result in movement ofthe syringe around the injection site after extraction and may causeshock to the subject receiving the injection.

Referring to FIGS. 18 to 21C, exemplary safety syringes are shown thatlimit and/or control the rate of extraction of a syringe needle from asubject. FIGS. 18A-C and 19A-C show one exemplary safety syringe 1800,and FIGS. 20A-C and 21A-C show another exemplary safety syringe 2000.Many of the features of the safety syringes of FIGS. 18A-C and 19A-C arethe same or similar to the features of other exemplary safety syringesdescribed herein. Therefore, not all of the features of the safetysyringes of FIGS. 18A-C and 19A-C are described here. The focus of thefollowing description is on the features of the safety syringes thatdiffer from features already described above. Other arrangements may beenvisaged within the scope of the appended claims.

FIGS. 18A-C show perspective views of the safety syringe 1800 atdifferent stages of operation. FIGS. 19A-C show sections through thesafety syringe 1800 at corresponding stages of operation.

Referring to FIG. 18A, the safety syringe 1800 comprises a ratecontrolling means. The rate controlling means comprises a ratecontrolling member 1851 having a first screw thread 1853 and acorresponding second screw thread 1855 configured to engage the firstscrew thread 1853.

The rate controlling means is configured to limit and/or control therate of extraction of a needle 1802 from a subject. The rate controllingmember 1851 of FIG. 18A forms part of a safety plunger 1810 and isconfigured to engage with a syringe plunger 1808 and, specifically, theexemplary rate limiting member 1851 shown is configured to extend intothe syringe plunger 1808. The engagement of the rate limiting member1851 with the syringe plunger 1808 is configured to limit and/or controlthe rate of relative motion between the safety plunger 1810 and thesyringe plunger 1808 after decoupling. In the exemplary safety syringeof FIG. 18A, the engagement between the rate limiting member 1851 andthe syringe plunger 1808 is configured to limit and/or control the rateat which the rate limiting member 1851 is able to enter the syringeplunger 1808.

The rate limiting member 1851 comprises a screw thread 1853 configuredto engage with a corresponding screw thread 1855 (shown in FIG. 19A) onthe syringe plunger 1808.

While the safety plunger 1810 and the syringe plunger 1808 are coupled,as in FIGS. 18A and 19A, they travel together on application of a forceto the safety plunger 1810.

FIGS. 18B and 19B show the point at which the safety plunger 1810decouples from the syringe plunger 1808.

After decoupling, the safety plunger 1810 is free to move relative tothe syringe plunger 1808 and, specifically, to move towards the needleend of the safety syringe 1800 while the syringe plunger 1808 remainssubstantially stationary, with respect to longitudinal movement. Uponthe application of further force to the safety plunger 1810 afterdecoupling from the syringe plunger 1808, the rate limiting member 1851begins to travel within the syringe plunger 1808, as shown in FIGS. 18Cand 19C. The screw thread 1853 on the rate limiting member 1851interacts with the screw thread 1855 in the syringe plunger 1808 toimpart a rotational force. The rotational force causes the syringeplunger to rotate within a barrel 1804 of the safety syringe 1800.

The rotation of the syringe plunger 1808 within the barrel 1804 isresisted by a friction between a bung 1857 and an inner surface of thebarrel 1804 and this limits and/or controls the rate of movement of thesafety plunger 1810 after decoupling from the syringe plunger 1808.

The bung 1857 may be formed of a resiliently deformable material, suchas a rubberised material, and has a diameter slightly larger than aninternal diameter of the barrel 1804, such that a seal is formed whenthe bung 1857 is inserted within the barrel 1804. That seal may alsoprovide resistance to the rotational motion of the syringe plunger 1808within the barrel 1804. Alternatively or in addition, the screw threads1853, 1855 may be configured to resist rotational motion of the syringeplunger 1808 for example by friction between the screw threads 1853,1855 themselves. The interacting surfaces of the screw threads 1853,1855 may be configured to provide a particular friction force.Alternatively or in addition, the syringe plunger 1808 may not be fixedto the bung 1857 and may be free to rotate therein. In sucharrangements, at least part of the force resisting rotation of thesyringe plunger 1808 may be provided by friction between the syringeplunger 1808 and the bung 1857.

FIG. 20A shows an end elevation of the handle portion 1811. FIG. 20Bshows a perspective view of a syringe plunger 1808 partially passedthrough the handle portion 1811. FIG. 20C shows a section through asyringe plunger 1808 fully passed through a handle portion 1811. Forclarity, FIGS. 20A-C do not show any other features of the safetysyringe 1800.

In exemplary apparatus, the safety plunger 1810 may be coupled to thesyringe plunger 1808 by a rotation prevention member 1860 configured toprevent rotation of the syringe plunger 1808 along at least part of itsinward stroke. As rotation of the syringe plunger 1808 under the forceapplied to the rate limiting member 1851 (and in exemplary apparatus,the screw thread 1853) is prevented, the syringe plunger 1808 movesalong its inward stroke under a force applied to the safety plunger1810. The syringe plunger 1808 and the safety plunger 1810 are thereforecoupled, as they move together on an inward (or outward) stroke.

In exemplary apparatus, the rotation prevention member 1860 may comprisea keyed aperture 1862 in a handle portion 1811 of the safety syringe1800. The keyed aperture 1862 comprises keying features 1864 a-b thatcorrespond to keying features 1866 a-b on the syringe plunger 1808, suchthat rotation of the syringe plunger 1808 is prevented when the keyingfeatures 1866 a-b of the syringe plunger 1808 engage with the keyingfeatures 1864 a-b of the handle portion 1811, as shown in FIG. 20B.

The syringe plunger 1808 decouples from the safety plunger 1810 when thesyringe plunger 1808 is released from the rotation prevention member1860. In exemplary apparatus, this may be provided by the keyingfeatures 1866 a-b of the syringe plunger 1808 no longer engaging withthe keying features 1864 a-b of the handle portion 1811. For example,the syringe plunger 1808 may comprise keying features 1866 a-b over onlypart of its length and once those keying features 1866 a-b have passedthrough the aperture 1862, the syringe plunger 1808 may be free torotate. Alternatively, and as shown in FIGS. 20A-C, a head 1868 of thesyringe plunger 1808 may be configured such that it can pass through theaperture 1862. In exemplary syringe plungers 1808, the head 1868 mayhave the same cross section as the region of the syringe plunger 1808comprising the keying features 1866 a-b. Therefore, the syringe plunger1808 is configured to pass through the aperture 1862 completely, asshown in FIG. 20C.

When the syringe plunger 1808 has passed through the aperture 1862 thekeying features 1866 a-b of the syringe plunger 1808 are no longerengaged with the keying features 1864 a-b of the aperture 1862 and thesyringe plunger 1808 is free to rotate. At this point, the syringeplunger 1808 and the safety plunger 1810 are decoupled.

It is noted that the term “decoupled” as used herein encompasses anysituation in which relative motion is permitted between a syringeplunger and a safety plunger. In specific apparatus, the relative motionmay be relative longitudinal motion. This applies to all apparatusdisclosed herein. That is, a syringe plunger does not need to bedetached or separated from a safety plunger in order to be decoupledfrom it. Further, there may still be some movement of a safety plungeralong its inward (or outward) stroke after decoupling, but there is adifference between a rate of movement between a safety plunger and asyringe plunger. For example, in the apparatus of FIGS. 18A-C and 19A-C,there may be some longitudinal movement of the syringe plunger along theinward stroke as well as rotational movement within the barrel afterdecoupling.

Referring to FIG. 21, an exemplary safety syringe 2000 is shown and isconfigured to limit and/or control a rate of extraction of a needle 2002from a subject after decoupling of a safety plunger 2010 and a syringeplunger 2008. The safety syringe comprises a rate controlling means 2051a, 2051 b configured to limit and/or control a rate of travel of thesafety plunger 2010 along its inward stroke after decoupling. The ratecontrolling means 2051 a, 2051 b comprises a resiliently deformable ratecontrolling projection 2051 a and a deforming surface 2051 b. The ratecontrolling projection 2051 a is located on a handle portion 2006 andprojects inwardly towards a longitudinal axis of the safety syringe2000. The rate controlling projection 2051 a may be the same or similarto the projection 1788 shown in FIG. 17.

The deforming surface 2051 b is configured to deform the ratecontrolling projection 2051 a as it passes over the deforming surface2051 b. In the exemplary safety syringe 2000, the deforming surface 2051b is located on the safety plunger 2010 and is configured to deform therate controlling projection 2051 a such that the force required to movethe safety plunger 2010 along its inward stroke after decoupling isincreased. In the exemplary safety syringe 2000 of FIGS. 21 and 22, thedeforming surface comprises a tab extending outwardly away from thelongitudinal axis of the safety syringe 2000. In the exemplary safetysyringe 2000, a tab is located on each arm 2116 a, 2116 b of the safetyplunger 2010. Each tab has a corresponding rate controlling projection2051 a. The tabs are positioned such that the rate controllingprojections 2051 a are deformed by the deforming surface 2051 b afterdecoupling of the safety plunger 2010 from the syringe plunger 2008. Inthis way the rate of extraction of the needle 2002 from the subject maybe controlled, e.g. decreased.

The operation of the safety syringe 2000 is now described with referenceto FIGS. 22A-C. In FIG. 22A, the safety syringe 2000 is shown in theextended state and with the safety plunger 2010 and the syringe plunger2008 coupled. The rate controlling projections 2051 a are located inrecesses 2059. This has the effect of locking the safety syringe 2000 inthe extended state. The recesses 2059 are configured to prevent furtherextension of the safety syringe 2000 and to require an initial force toovercome a threshold before an inward stroke of the safety plunger 2010and the syringe plunger 2008 can begin.

After the threshold force is overcome, the rate controlling projections2051 a are deformed and the safety plunger 2010 and the syringe plunger2008 begin to move along their inward strokes. At a point along theinward strokes, the safety plunger 2010 and the syringe plunger 2008become decoupled, using any method discussed above.

In FIG. 22B, the safety syringe 2000 is shown shortly after decouplingand the rate controlling projections 2051 a are shown in contact withthe deforming surfaces 2051 b. The rate controlling projections 2051 aare further deformed by the deforming surfaces 2051 b and thereforeexert a force on the arms 2116 a, 2116 b of the safety plunger 2010 byway of the deforming surfaces 2051 b. The increased force applied by therate controlling projections 2051 a on the arms 2116 a, 2116 b increasesfriction between the rate controlling projections 2051 a and thedeforming surfaces 2051 b and the rate of extraction of the needle 2002from the subject is thereby limited and/or controlled.

In FIG. 22C, the safety syringe 2000 has completed its inward stroke andthe rate controlling projections 2051 a have passed over the deformingsurfaces 2051 b and snapped back into locking recesses 2061 on the arms2116 a, 2116 b. The locking recesses 2061 are configured to prevent theoutward movement (i.e. extension) of the safety plunger 2010.

Exemplary safety syringes and safety syringe apparatus may be providedas a kit of parts for assembly. The kit of parts may comprise aplurality of elemental parts for assembly or may comprise a one or morecomposite parts (or sub-assemblies) that are pre-assembled.

Broadly, exemplary apparatus disclosed herein may comprise four parts: asafety plunger; a syringe plunger; a handle portion; and a sheath. Theseparts may be single moulded elements or may be constructed from aplurality of moulded elements. The four parts may be provided as one ormore sub-assemblies.

For example, the safety plunger, syringe plunger and handle portion maybe provided as a first sub-assembly. The first sub-assembly may beprovided in a kit of parts with a sheath. In such configurations, asafety syringe may be assembled by positioning a pre-loaded syringebarrel into the first sub-assembly and then connecting the sheath to thefirst sub-assembly. Alternatively, the syringe barrel may be positionedwithin the sheath and the sheath may then be connected to the firstsub-assembly.

In another example, the safety plunger and the syringe plunger may beprovided as a second sub-assembly. The second sub assembly may beprovided along with the handle portion and the sheath in a kit of parts.In such arrangements, the safety syringe may be assembled by connectingthe second subassembly to the handle portion, positioning a pre-loadedsyringe barrel into the handle portion and second sub-assembly and thenconnecting the sheath to the handle portion and second sub-assembly.Alternatively, the syringe barrel may be positioned within the sheathand the sheath may then be connected to the handle portion and thesecond sub-assembly.

In another example, each of the four parts may be supplied separately asa kit of parts. In such arrangements, the safety plunger, syringeplunger and handle portion may all be connected together. A pre-loadedsyringe barrel may be connected to the assembled safety plunger, syringeplunger and handle portion, and the sheath may then be connected to theassembled safety plunger, syringe plunger and handle portion.Alternatively, the syringe barrel may be positioned within the sheathand the sheath may then be connected to the assembled safety plunger,syringe plunger and handle portion.

Various exemplary safety syringes described herein provide a lockingmeans to lock the safety syringes in an extended state. The safetysyringes may be supplied to a medical professional preloaded with amedicament and in the extended state. The locking means allows themedical professional to handle the safety syringe by the safety plungerand/or the syringe plunger, as the safety plunger and syringe plungerare prevented from further extension by the locking means.

The locking means also allows exemplary safety syringes to beauto-disabling. Such safety syringes may comprise a syringe plunger thatis not physically connected to the bung. Rather, an end of the syringeplunger abuts the bung without being attached. In this configuration,the syringe plunger is able to push the bung into the barrel of thesyringe in order to expel the contents of the barrel, but if the syringeplunger is withdrawn from the barrel it is disengaged from the bung,which is left in the barrel. Such safety syringes cannot be re-used, asthe bung is trapped within the barrel and are therefore consideredauto-disabling. The locking means provided on various exemplary safetysyringes allows the auto-disabling feature, as the syringe plungercannot be extended further than the locking means will permit and istherefore held in contact with the bung without needing to be secured toit.

It is noted that many of the features of the exemplary apparatusdescribed above and shown in the drawings may be included in otherexemplary apparatus. As such, the different drawings are not necessarilyto be considered as separate embodiments and features from one drawingmay be transferred to an apparatus in another drawing. It is also notedthat any of the features of the safety syringes described herein may beused in a safety syringe apparatus for fitting to a syringe.

The skilled person will be able to envisage other safety syringes andfeatures thereof without departing from the scope of the appendedclaims. In particular, it is noted that one or more features included inone or more drawings may be integrated into safety syringes shown inother drawings, as will be appreciated by the skilled person.

The invention claimed is:
 1. A safety syringe comprising: a barrelhaving an opening at an end thereof; a syringe plunger configured tomove within the barrel to cause a substance within the barrel to beexpelled from the opening; a safety plunger coupled to the syringeplunger such that an inward stroke of the safety plunger causes thesyringe plunger to move forward within the barrel; first keying featuresengaged with second keying features of the syringe plunger, such thatrotation of the syringe plunger is prevented; and a sheath configured tobe deployed by the safety plunger so as to cover at least partially theopening in the barrel after use of the syringe, wherein the safetyplunger is configured to decouple from the syringe plunger at a point onthe inward stroke under rotation of the syringe plunger relative to thesafety plunger upon disengagement of the first and second keyingfeatures, such that the safety plunger is moveable further forwardindependently of the syringe plunger, and wherein further forwardmovement of the safety plunger after decoupling causes the sheath atleast partially to cover the opening in the barrel.
 2. The safetysyringe as claimed in claim 1, wherein the first keying featurescomprise a keyed aperture through which the syringe plunger passes. 3.The safety syringe as claimed in claim 2, wherein the first keyingfeatures comprise one or more straight edges of the keyed aperture. 4.The safety syringe as claimed in claim 3, wherein the keyed aperture isgenerally circular, and wherein the one or more straight edges areformed by a chord of the generally circular keyed aperture.
 5. Thesafety syringe as claimed in claim 2, wherein the syringe plunger isconfigured to pass through the keyed aperture completely to decouple thesyringe plunger from the safety plunger.
 6. The safety syringe asclaimed in claim 1, wherein the second keying features are formed alongan outer surface of the syringe plunger.
 7. The safety syringe asclaimed in claim 6, wherein the second keying features comprise one ormore flat outer surfaces extending along at least part of a length ofthe syringe plunger.
 8. The safety syringe as claimed in claim 7,wherein the syringe plunger is generally circular, and wherein the oneor more flat outer surfaces are formed by a chord of the generallycircular syringe plunger.
 9. The safety syringe as claimed in claim 1,wherein the syringe plunger comprises at least one rotation surfaceconfigured to rotate the syringe plunger for a portion of the inwardstroke of the safety plunger.
 10. The safety syringe as claimed in claim9, wherein the further forward movement of the safety plunger afterdecoupling causes the syringe plunger to rotate within the barrel. 11.The safety syringe as claimed in claim 10, wherein the syringe plungerremains substantially stationary with respect to longitudinal movementafter decoupling.
 12. The safety syringe as claimed in claim 9, whereinthe syringe plunger comprises a first screw thread configured tointeract with a second screw thread of the safety plunger to rotate thesyringe plunger after decoupling.
 13. The safety syringe as claimed inclaim 1, further comprising a resiliently deformable bung within thebarrel.
 14. The safety syringe as claimed in claim 13, wherein theresiliently deformable bung is configured to allow relative rotationbetween the resiliently deformable bung and the syringe plunger, andwherein a friction force between the syringe plunger and the resilientlydeformable bung resists rotation of the bung and the syringe plunger.15. The safety syringe as claimed in claim 1, wherein decoupling issubstantially at a point at which the syringe plunger has reached theend of the barrel.
 16. The safety syringe according to claim 1, furthercomprising a handle portion, which includes the first keying features.17. The safety syringe as claimed in claim 16, wherein the handleportion is fixed relative to the barrel.
 18. A safety syringe apparatusfor use with a syringe, the syringe comprising a barrel having anopening at an end thereof, the syringe apparatus comprising: a syringeplunger configured to move within the barrel to cause a substance withinthe barrel to be expelled from the opening; a safety plunger coupled tothe syringe plunger such that an inward stroke of the safety plungercauses the syringe plunger to move forward within the barrel; firstkeying features engaged with second keying features of the syringeplunger, such that rotation of the syringe plunger is prevented; and asheath configured to be deployed by the safety plunger so as to cover atleast partially the opening in the barrel after use of the syringe,wherein the safety plunger is configured to decouple from the syringeplunger at a point on the inward stroke under rotation of the syringeplunger relative to the safety plunger upon disengagement of the firstand second keying features, such that the safety plunger is moveablefurther forward independently of the syringe plunger, and whereinfurther forward movement of the safety plunger after decoupling causesthe sheath at least partially to cover the opening in the barrel.
 19. Akit of parts for assembly into a safety syringe apparatus for use with asyringe, the syringe comprising a barrel having an opening at an endthereof, and a syringe plunger configured to move within the barrel tocause a substance within the barrel to be expelled from the opening, thekit of parts comprising: a safety plunger coupled to the syringe plungersuch that an inward stroke of the safety plunger causes the syringeplunger to move within the barrel; first keying features engaged withsecond keying features of the syringe plunger, such that rotation of thesyringe plunger is prevented; and a sheath configured to be deployed bythe safety plunger so as to cover at least partially the opening in thebarrel after use of the syringe, wherein the safety plunger isconfigured to decouple from the syringe plunger at a point on the inwardstroke under rotation of the syringe plunger relative to the safetyplunger upon disengagement of the first and second keying features, suchthat the safety plunger is moveable further forward independently of thesyringe plunger, and wherein further forward movement of the safetyplunger after decoupling causes the sheath at least partially to coverthe opening in the barrel.
 20. The kit of parts as claimed in claim 19,further comprising a syringe.